Ecological impact of changes in intrinsic growth rates of species at different trophic levels

Decreased and increased intrinsic growth rate and abundance of a single species can severely and negatively impact other species in the same food web. Here we compare the wider system effects of decreased and increased intrinsic growth rates of species occupying different trophic levels. Specifically, we derive the change in growth rate of a single (focal) species necessary to cause a 90% reduction in the abundance - a quasi-extinction - of another species in model communities. We find that even relatively small changes, negative as well as positive, in the growth rate of the focal species can cause quasi-extinctions of others. Furthermore, the magnitude of change needed to cause a quasi-extinction depends on the trophic level of the perturbed species. The potential ecosystem impact of such 'negative' and 'positive' changes is largely unknown. We argue that such a targeted decrease or increase could be induced by human interference, such as hunting or harvesting, but also by an outbreak or fade-out of an infectious disease. As ecosystems maintain many and diverse infectious agents, these results suggest that these agents may play an important role in the structure and balance of ecosystems

The Effectiveness of Contact Tracing in Emerging Epidemics

BACKGROUND: Contact tracing plays an important role in the control of emerging infectious diseases, but little is known yet about its effectiveness. Here we deduce from a generic mathematical model how effectiveness of tracing relates to various aspects of time, such as the course of individual infectivity, the (variability in) time between infection and symptom-based detection, and delays in the tracing process. In addition, the possibility of iteratively tracing of yet asymptomatic infecteds is considered. With these insights we explain why contact tracing was and will be effective for control of smallpox and SARS, only partially effective for foot-and-mouth disease, and likely not effective for influenza. METHODS AND FINDINGS: We investigate contact tracing in a model of an emerging epidemic that is flexible enough to use for most infections. We consider isolation of symptomatic infecteds as the basic scenario, and express effectiveness as the proportion of contacts that need to be traced for a reproduction ratio smaller than 1. We obtain general results for special cases, which are interpreted with respect to the likely success of tracing for influenza, smallpox, SARS, and foot-and-mouth disease epidemics. CONCLUSIONS: We conclude that (1) there is no general predictive formula for the proportion to be traced as there is for the proportion to be vaccinated; (2) variability in time to detection is favourable for effective tracing; (3) tracing effectiveness need not be sensitive to the duration of the latent period and tracing delays; (4) iterative tracing primarily improves effectiveness when single-step tracing is on the brink of being effective

Wild Birds and Increased Transmission of Highly Pathogenic Avian Influenza (H5N1) among Poultry, Thailand

Wild birds are associated with increased virus spread to poultry

Methicillin-resistant staphylococcus aureus nosocomial infection has a distinct epidemiological position and acts as a marker for overall hospital-acquired infection trends

An ongoing healthcare debate is whether controlling hospital-acquired infection (HAI) from methicillin-resistant Staphylococcus aureus (MRSA) will result in lowering the global HAI rate, or if MRSA will simply be replaced by another pathogen and there will be no change in overall disease burden. With surges in drug-resistant hospital-acquired pathogens during the COVID-19 pandemic, this remains an important issue. Using a dataset of more than 1 million patients in 51 acute care facilities across the USA, and with the aid of a threshold model that models the nonlinearity in outbreaks of diseases, we show that MRSA is additive to the total burden of HAI, with a distinct 'epidemiological position', and does not simply replace other microbes causing HAI. Critically, as MRSA is reduced it is not replaced by another pathogen(s) but rather lowers the overall HAI burden. The analysis also shows that control of MRSA is a benchmark for how well all non-S. aureus nosocomial infections in the same hospital are prevented. Our results are highly relevant to healthcare epidemiologists and policy makers when assessing the impact of MRSA on hospitalized patients. These findings further stress the major importance of MRSA as a unique cause of nosocomial infections, as well as its pivotal role as a biomarker in demonstrating the measured efficacy (or lack thereof) of an organization's Infection Control program

The circulation of Anaplasma phagocytophilum ecotypes is associated with community composition of vertebrate hosts

Anaplasma phagocytophilum is a tick-borne pathogen that has been detected in many tick and vertebrate species. It is among the most widespread tick-borne pathogens in animals in Europe. The bacterium can be genetically divided into four ecotypes, which are linked to distinct but overlapping host species. However, knowledge about the transmission dynamics of the enzootic cycles of the different ecotypes is limited. Here, we quantified the link between the ecotypes of A. phagocytophilum, the different life stages of the tick Ixodes ricinus, and vertebrate host groups through a meta-analysis. We extracted data on the mean I. ricinus burden and the A. phagocytophilum infection prevalence in both hosts and feeding I. ricinus from 197 papers on 77 wildlife species. With this information, we modeled the relative importance of different host taxonomic groups for the circulation of the different ecotypes of A. phagocytophilum in a theoretical assemblage of hosts with varying presence of red deer (Cervus elaphus) and densities of small mammals. We showed that the composition of the vertebrate community affects the relative abundance of different ecotypes of A. phagocytophilum in the different life stages of I. ricinus. The presence of red deer is likely to increase the infection prevalence of Ecotype 1 in ticks, while small mammal densities drive the prevalence in ticks of mainly Ecotype 3, and to a lesser extent Ecotype 1. In Europe, vertebrate communities are changing, with an increase in red deer abundance and changes in the population dynamics of small mammals. Our results suggest that these changes could imply an increase in the circulation of A. phagocytophilum and thus an increase in the risk for public and veterinary health